Piezo-electric transmitter and recorder



Nov. 13, 1934.

A. A. THOMAS PIEZO ELECTRIC TRANSMITTER AND RECORDER INVENTOR Original Filed Sept. 22, 1928 Patented Nov. 13, i 1934 maze-anaemic ramsmma mm I aacoanaa Adolph A. Thomas, New York, 1.

Application September 22, 1928, semi No. 307,749 I Renewed September 26, 1933 17 Claims. (cl. ire-11o) My. invention relates to the art of transmitting and re'cordihg sound by utilizing the so-called piezo-electric properties of certain crystals adapt edto vibrate physically when subjected to vari-' 5 able electric pressure. v

In one form of my invention, a piezo-electric crystal actuates a vibratory member, which, is

preferably; a spring arm or other elastic support carrying an operative element. For electrically transmitting and amplifying the movements of the crystal, the operative element carried by the vibratory spring arm may be a small mirror,

in accordance with transmitted sound. The sound waves to be recorded are converted into electric impulses which are impressed upon the crystal, and the vibrations of the crystal aretransmitted in predetermined ratio to the recording tool. In-' stead of mounting the recording tool on a separate support, as described, I may attach it directly to the crystal.

' The objects and practical advantages of my invention will be understood from a detailed description of the accompanying drawing, in

which- V Fig. 1 illustrates diagrammatically a soundtransmitting system embodying the idea of my invention;

Figs. 2 and 3 are, respectively, side and plan views of a piezo electric crystal arranged to actuate a recording tool for lateraL-cut records;

Fig. 4 is a view similar to Fig. 3', except that the recording tool is arranged to operate on vertical-cut records; a

Fig. 5 shows a piezo-electric crystal carrying a recording tool for lateral-cut records; and

Fig. 6 shows a piezo-electric crystal carrying a recording tool for vertical-cut records.

Referring to Fig. 1, there is a piezo-electric crystal 10 mounted 'at one ,end in a rigid support 12, which is .diagrammatically indicated as a block, but which may be any suitable structure. The crystal is connected in a transmitting circuit 13 adapted to convert sound into variable electric impulses, which are impressed upon the crystal at electrically opposite points 14 and 15. It will be understood that the crystal 10 and transmitting circuit 13 are shown merely in a diagrammatic way to make the drawing as simple and clear as possible. The transmitting circuit includes a suitable source of electric energy 16, conventionallyrepresented as a battery, and a telephone transmitter 17 operates to vary the voltage at points 14 and 15 in accordance with the transmitted sound. The element 10 is intended to represent a piezoelectric crystal of any suitable type or any operative section of such crystal. Among crystals possessing a piezo-electric character I may mention quartz, fluorspar, topaz, tourmaline and Rochelle salt. Perhaps the two most practical crystals are quartz and Rochelle salt, the latter being piezoelectric in a greater degree than the others. While quartz is only moderately piezo-electric, it possesses a mechanical strength that gives it certain advantages over other crystals. The selection of a suitable crystal or section of crystal lies withinthe skill of the experimenter. The leads of circuit 13 are electrically connected to the crystal 10 in any practical way, as by means of tin foil coatings attached to opposite poles or faces of the crystal. One of these terminal coatings is indicated in outline at 18. The points at which the a set-screw 22 secures the arm in adjusted posi- 105 crystal is connected in circuit will manifestly depend upon the particular kind of crystal used. Forexample, in Fig. 1 the piezo-electric element 10 is supported to represent a crystal (or part of a crystal) of Rochelle salt, in which the, free end lo forms a positive pole and the central part a negative pole. Consequently, when a variable electric pressure is applied, the crystal vibrates mechanically-in accordance with the impressed voltage. The support 12 in which one end of the crystal is rigidly mounted should be sufliciently heavy and solid to be non-vibratory, so that the free end 10 of the crystal may vibrate in the-direction of its length or longitudinal axis.

A vibratory member 19, which I haveshown inthe form or a spring arm, is mounted at one end on a suitable support 20, which has a slot 21 for receiving the spring arm 19 in a tight lit. The arm 19 is longitudinally adjustable in slot 21, andv m y be regulated in any suitable way-for in- 110 stance, by adjusting either of the supports 12 and relatively to the other.

The spring arm 19 carries a tiny mirror 23, which is attached to the face of the arm by cement or in any other practical'way. It is evident that the transmission ratio between the crystal 10 and mirror 23 depends upon the distance of the mirror from the effective pivot point fective length of arm 19, the degree of amplification (or reduction) of the mirror movements may be regulated to obtain the best results in any given case. -When a variable potential is impressed on crystal 10 by electric impulses produced in circut 13, the crystal vibrates in the direction of its length, and thereby actuates the resilient arm 19 and the attached mirror 23.

A photo-electric cell or any practical construction is diagrammatically indicated at 24 and has the usual electrodes 25 and 26. The electrode 25 represents the anode of the cell and is usually in the form of a grid, while the electrode 26 is the cathode which is constructed of (or coated with) light-sensitive material adapted to emit electronsin the operationof the cell. There are various makes of photo-electric cells on the market, and their construction is well understood. In one form of cell known to the public, the cathode consists of a plate carrying a deposit of alkali metal which has the property of releasing electrons in accordance with the amount or intensity of light that strikes the cathode at any instant. In other words, the output of the cell depends upon the degree of illumination impressed upon .the cathode.

The mirror 23 and cell 24 are so arranged that a beam of light from a lamp 2'? falls on the mirror and is reflected upon cathode 26, as indicated by lines 28. Condensing lenses 29 concentrate the light from the lamp 27 as a spot on mirror 23 and electrode 26. The lamp 27 is preferably an electric bulb of proper constant light intensity, but any other suitable source of illumination may be employed. It is clear that, when the mirror 23 vibrates, the amount of light thrown on cathode 26 is correspondingly varied. The cathode 26 is connected by a conductor 30 to the grid 31 of an amplifier tube V; which also has the usual filament 32 and plate 33. A battery A heats the filament, and a battery B feeds the plate circuit, which includes an operative coil 34. In the present instance, the coil 34 represents theprimary of a transformer T, the secondary 35 of which con-, trols or operates suitable mechanism R. When my invention is used for sound recording, the mechanism R represents any practical construction of recording tool adapted to be operated by current impulses in the secondary coil 35. When the sounds that actuate the transmitter 17 are 1 to be broadcast, mechanism R.may be regarded as diagrammatically representing suitable broadcasting or radio receiving apparatus. A battery 36 is connected at the positive pole to theanode 25 of photo-electric cell 24, and the negative side I of the battery is connected to the filament 32 of The operation of the sound-transmitting system above described will be clear to those familiar ror 23, which represent the transmitted sound,

vary the quantity of light falling on cathode 26, The result is a corresponding change in the electronic output of the cell, whereby theresistance of the circuit of battery 36 is varied. The effect of this is to vary the potential on grid 31, which controls the current impulses in the plate circuit of tube V, as will be understood without further explanation. Therefore, the minute mechanical movements of crystal 10 are ultimately translated into current impulses in coil 35 sufiicient to operate a recording tool, a loudspeaker, or any other practical device.

In Figs. 2, 3 and 4 thevibratory spring arm 19 carries at its free end a recording tool 37 having a suitable cutting point 38 for indenting the surface 39 of a wax record blank mounted to rotate at the proper speed. The slotted support 20, in which the spring arm 19 is. adjustably mounted, is provided with an extension 40 to which one end of the piezo-electric crystal 10 is rigidly attached in any practical way. In Figs. 2 and 3, the recording tool 37 is so mounted on the spring arm 19 as to cut a lateral groove 41 in the disk record 39, while in Fig. 4 the recording tool is arranged to operate vertically for making vertical-cut records. The recording tool 37 is secured to the spring arm 19 by means of a slot 42 in which the end of the arm is immovably fitted, and oneor more rivets may be used to make the connection permanently rigid. The vibratory arm 19 is so arranged that it always presses against the free edgeof crystal 10, so that the cutting'tool may instantly respond to the crystal movements without lost motion. If desired, a contracting coil spring 43 may be employed as additional means for holding the vibratory member 19 in pressure screw to adjust the normal tension of spring 43 to the proper amount. The coil spring 43 may be encased in an elastic sleeve 48 to damp unneces' sary vibrations of the spring. The damping sleeve 48 may be a rubber tube stretched over the spring. If the coil spring 43 is used to hold the arm 19 pressed against the crystal, it is evident that the arm need not be flexible, for it may be a rigid bar pivoted at its rear end.

It will be noticed that in Figs. 2, 3 and 4 the vibrations of the piezo-electric crystal 10 are transmitted to the cutting point 38 in amplified ratio. If the cutting point is arranged between the crystal and the supporting point of arm '19,

the movements of they cutting point will be of smaller amplitude than those of the crystal. By mounting the cutting point 38 in alignment with the contact point between crystal l0 and arm 19, the movements of the crystal and the cutting point are of substantially equal amplitude. The best arrangement of the'parts can only be determined by actual experiment within the skill of the artisan to obtain the best results in anyparticular design of instrument. Since the moveway; as by cement or clamping.

- same as that of Fig. 5, the only difference being ments of crystal 10 are transmitted directly and without lost motion to the cutting point38, the transmitted sound is faithfully recorded. It is hardly necessary to add that the support 20 in Figs. 2, 3 and 4 is mounted at its other end to travel horizontally over the rotating record, so that the cutting point 38 may engrave a spiral groove in thesoftsurface of the recorded blank. In Fig. 5 the piezo-electric crystal 10 is supposed to representa slab or bar of quartz provided at opposite sides with thin conducting plates 49, usually tin foil, to which the circuit leads 50 are attached. One end of the crystal is rigidly mounted in a block 51 carried by an arm 52, which is supported at its other end to swing horizontally over a record. In this construction the recording tool 3'! is directly attached to the free end of crystal 10 in such a way that the cutting point 38 makes a lateral groove 53 in the rotating record. The recording tool 38 is fastened to the crystal in any practical The construction of Fig. 6 is practically the that the recording tool 3'7 is so mounted on the crystal'that the cutting point 38 makes a verticalcut spiral groove in the record. In other words.

' the crystal 10 in Fig. 5 vibrates in a direction substantially parallel with the surface of the blank recording disk, while in Fig. 6 the crystal is mounted to vibrate in a direction substantially vertical to theplane of the record blank.

The sound-actuated device 1'7 may be of any approved type adapted to produce variable electric pressure at the opposite poles of the piezo:

electric crystals shown in the various views. By

separating the crystal from the transmitter, it is possible to locate the crystal ina different room free from the disturbing vibratory effects of the sound waves that are being produced in another room for recording or broadcasting. In other words, the movements of mirror 23 and recorder 37 are mechanically independent of the transmitter vibrations. Further,the use of apiezoelectric crystal dispenses with electromagnetic mechanism heretofore employed for translating electric impulses into mechanical movements.

Thus, I have produced a sound-transmitting and I recording system of marked simplicity and improved operation.

When I speak ofa piezo-electric crystal in the description and the claims, I do not necessarily mean a complete crystal, but I include any part or section of a crystal that may be found to be operative. For instance, a plate, rod or bar may be cut from a crystaland used in constructing my invention. The dimensions of such a crystal section will depend upon. the kind and size of crystal used. Furthermore, thedirection of the most effectivemechanical and electrical strain in the crystal will vary with different kinds of crystals, so that the best way of mounting a crystal is often a matter of experimentation which may readily be carried out by those skilled in the art.

- When I, therefore, refer to opposite ends or poles of the'crystaL'I' mean any faces .or points between which electric pressure may be applied to produce, Physical movement of the crystal.

As I said before, the drawing has been made as simple as possible for the sake of clearness,

and it is therefore not to be considered in the nature of a shop drawing. It is rather a diagram.- matic representation in which no effort has been made to show mechanical details correctly. In

.Fig. 1, only such circuit connections are shown means of certain constructions and arrangements, I wish to be clearly understood that I have done so merely by way of illustration, and not as a restriction or limitation of my invention. It is obvious that the basic principle of my invention may be mechanically embodied in other ways and by other means than herein set forth.

This application is a continuation in part of my copending application filed September 24, 1926 now Patent Number 1,760,383 granted May 27, 1930.

I claim as my invention:

1. The combination of a piezo-electric crystal mounted for vibratory movement, a mirror supported independently of said crystal and vibrated by the movements thereof in predetermined transmission ratio, and manually operable means for varying said transmission ratio.

2. The combination of a support, a vibratory spring blade mounted at one end on said support and adjustable lengthwise thereon to change its effective length, piezo-electric means for actuating said spring blade, and a member operated by ,the movements of said blade:

3. In an electric vibratory system, a fulcrumed arm carrying an operative element permanently mounted thereon, a piezo-electric crystal movable substantially at right angles to the length of said arm for actuating the same, and means for regulating the distance between said element and the fulcrum of said arm, said regulating means being operable without adjusting the position of said element on its supporting arm.

4. In an electric vibratory system, the combination of a support, a vibratory arm fulcrumed to said support, piezo-electric means for actuating said arm,astylus fixed on said arm, and means for adjusting said arm lengthwise on said support to vary the position of its fulcrum in relation to said stylus, said adjusting element being operable without altering the position of the stylus on its supporting arm.

5. The combination of a piezo-electric crystal mounted for vibratory movement, a vibratory member supported independently of said crystal and actuated by the movements thereof, an operative element mounted on said member, and manually controllable means independent of said element for regulating the transmission ratio between said crystal and said element, said regulating means. being operable without adjusting the position of said element on its supporting member.

6. The combination of a piezo-electric crystal, a springarm arranged to be constantly in mechanical pressure contact with said crystal to vibrate therewith, an operative element mounted on said arm, and means for adjustably mounting said spring arm to regulate its effective length.

7. The combination of a piezo-electric. crystal mounted for vibratory movement, a vibratory member mounted independently of said crystal and actuated by the movements thereof, an operative element carried by said member, and means for adjusting said memberlaterally of said crystal to vary the transmission ratio between said crystal and said element.

8. The combination of a piezo-electric crystal mounted to vibrate in'accordance with electricimpulses in a circuit, a record-engaging element actuated by said crystal at a different amplitude from the crystal vibrations, a support on which said 'element is mounted independently of said crystal, andmeans independent of said element for regulating the amplitude of vibration of said element relatively to the amplitude of the crystal vibrations, said regulating means being operable without adjusting the position of said element on its support.

9. The combination of a piezo-electric crystal, a movable member constantly in. mechanical pressure contact with said crystal to vibrate therewith, a phonographic recording tool connected to said member, for making lateral-cut records on a disk, and means whereby the vertical pressure on said tool during the recording operation is not communicated to said crystal.

10. The combination of a piezo-electric'crystal, a phonographic recording tool mechanically operated by the movements of said crystal, means whereby the vibrations of said tool are of different amplitude from the crystal vibrations, and means movable substantially at right angles to the vibration axis of said crystal for varying said amplitude.

11. In phonographic recording apparatus, the combination of a piezo-electric crystal, 2. movable member arranged to be constantly in mechanical pressure contact with said crystal to,

vibrate therewith, a recording tool carried by said member, and means independent of said tool for regulating the transmission ratio be- I tween said crystal and said tool, said regulating means being operable without adjusting the position of said tool on its supporting member.

12. The combination of a piezo-electric crystal, a recording stylus actuated by said crystal, 2.

support for said stylus, and manually adjustable means independent of said stylus for regulating the amplitude of the stylus vibrations relatively to the amplitude of the crystal vibrations, said ed for lateral vibratory movement to produce a" lateral-cut sound groove in a phonograph disk, and piezo-electric means mounted horizontally over said disk and substantially parallel therewith for operating said tool, which is supported independently of said means.

14. In an electric vibratory system, a vibratory arm carrying an operative element, a now-vibratory support for said arm, a piezo-electric crystal for actuating said arm, and means independent of said element for varying the eiiective length or said arm.

15. Tire combination of vibratory piezo-electric means, an element actuated by said means, and means for regulating the vibration amplitude of said element relatively to the vibration amplitude of said piezo-electric means. I

16. The combination of a piezo-electric crystal, a mirror vibrated by said'crystal, and means for regulating the amplitude of the mirror yibrations relatively to the amplitude of the crystal vertically over said disk for operating said tool,

which is supported independently of said means.

' ADOLPH A. THOMAS.

no I 

